1. Field of the Invention
The present invention relates to an improvement of a remotely operated circuit breaker, and more particularly to a remotely operated circuit breaker capable of being frequently operated with a long working life.
2. Background Art
FIG. 8 shows a prior art wiring flow diagram for a conventional three phase induction motor M. The induction motor M is connected to a power source (not shown) through a main-circuit open/close appliance in which independent circuit breakers 1 are connected in series with electromagnetic contactors 2 and inserted in each of three power lines connected to the power source.
The circuit breakers 1 and contactors 2 are so connected because the circuit breakers 1 are intended to protect the power line and electric equipment such as the main circuit appliances and the motor M from short-circuit or overload. The circuit breakers 1 are therefore designed to be operated less than 10,000 times. Thus, the breaker 1 is not suitable for switching the main power of the appliance where on/off operation of the circuit is very frequent. In addition, it is difficult to remotely operate the breaker.
Thus the electromagnetic contactors 2 are used for applications where circuits are frequently opened or closed. However, in the case where the contactors alone are used in the circuit, once a large current flows therethrough due to, for example, short-circuit or overcurrent in excess of the rated power of a load, the large current causes the contacts to melt, rendering the contacts useless. One way of overcoming the aforementioned drawbacks is to cascade the breakers 1 and the electromagnetic contactors 2 in series, permitting highly frequent and remote on-and-off operations of the circuit as well as the electrical contacts are prevented from melting.
In the case where the breakers 1 and the electromagnetic contactors are to be housed in a housing 3, not only they must be manufactured separately but also mounting the breakers and contactors and wiring between the electromagnetic contactors and the circuit breakers are complex. Further, a large space is required in the housing 3, leading to a large size of the breaker apparatus.